Door checks which provide for limited opening of a door, by use of a hasp hinged on a vertical axis and slotted to receive a headed slide bolt which projects from a housing mounted on the door projecting across the door edge, are well known. It is conventional that the housing which bears the slide bolt may have a flat inward vertical surface against which the hasp may be folded, the housing wall having a thumb screw over which the slot of the hasp may pass, to be turned to retain the hasp against the inner surface of the housing and thus serve as an additional locking device.
That construction permits only one extent of door opening. Hasp type devices have been patented, however, which permit at least two extents of door opening, for example, a narrow opening through which the persons inside and outside the door may converse or through which a letter may be passed, and a larger opening through which a small package may be passed; but such devices involved increased complexity. For example U.S. Pat. No. 1,785,772 to Hallman makes provision for hinging the plate which mounts the hasp to the door jamb, so that the hasp axis may be rotated out of vertical; and a somewhat similar provision is made in U.S. Pat. No. 179,308 to Hill. U.S. Pat. No. 197,577 to Whipple adds an axially sliding bolt to achieve retention in more than one position along the slotted hasp. In each of these devices, the slot in the hasp has but a single width, interrupted by notches which make possible the multiplicity of positions.